The demand for automatic door and gate openers has increased rapidly during recent years for a number of reasons including the high cost of labor, convenience and security. Depending upon the particular installation, anyone of several different types of gates or doors may be employed, such as swinging single gates, opposed swinging gates, vertical roll-up doors, and horizontally traveling, track gates.
Control systems employed for operating these gates and doors normally include one or more sensors which automatically open and close the gate or door in response to the approach of a person or vehicle.
Gates and doors of the type described above are typically operated by a reversible electric motor, which in turn is operated by the control system. Some control systems may employ a plurality of manually actuable switches to allow the user to either open, close or stop the door or gate by actuating a single switch. Other systems employ a single manually actuatable switch which may be sequentially operated by the user to effect opening, closing or stopping of the gate or door. In some cases, door or gate operation is automatically effected by one or more remotely located switches which are automatically activated by a vehicle or person approaching or leaving the gate.
Various types of obstructions are encountered from time to time which may prevent the gate from opening or closing. When an obstruction is encountered by a gate, the load on the gate driving motor is substantially increased, thereby substantially increasing the level of electrical current flowing through the motor. It is normally desirable to interrupt movement of the gate/door when it encounters an obstruction, consequently, means must be provided for sensing the overcurrent condition and for de-energizing the driving motor shortly after the obstruction is encountered. Previous attempts at obstruction sensing have been mechanical in nature; prior protective devices consisted of mechanical clutches connecting the motor to the gate which released the connection when the mechanical load on the motor exceeded a prescribed value. These mechanical clutches are not only rather costly to manufacture, but also add to the overall bulk of the gate opener and are also subject to frequent mechanical failure as well as the need for periodic maintenance. Moreover, failure of these clutches to operate properly when an obstruction is encountered often results in permanent electrical damage to the motor.
Thus, there is a need in the art for a gate control system having electronic obstruction sensing which avoids each of the deficiencies of the prior art system discussed above.